The present invention relates to apparatus for perforating webs, sheets, strips or bands of flexible material, such as paper, imitation cork, cardboard, a synthetic plastic substance or the like. More particularly, the invention relates to improvements in apparatus which can be utilized with advantage to form perforations in a running (continuous or interrupted) web of cigarette paper or the like while the web is transported lengthwise in a cigarette making, filter tipping or other tobacco and/or filter material processing machine. Still more particularly, the invention relates to improvements in perforating apparatus wherein the means for forming perforations includes one or more devices for focusing one or more beams of coherent radiation onto the running web of paper or the like.
It is already known to form perforations in a web of cigarette paper, imitation cork or similar flexible strip, band or sheet material which is used in the manufacture of rod-shaped smokers' products. The perforations are desirable, especially if the permeability of the material of the web is not sufficiently high, in order to ensure that, when a smoker draws a column of tobacco smoke into his or her lungs, the smoke is mixed with a certain quantity of cool atmospheric air which penetrates into the interior of the smokers' product by way of the perforations and contributes to interception and/or neutralization of certain amounts of nicotine, condensate and/or other deleterious or presumably deleterious ingredients of tobacco smoke. For example, many types of filter cigarettes are formed with annuli of perforations which are provided in a short tube serving to connect the filter plug to the tobacco-containing portion of the cigarette. The tube is a converted uniting band which is obtained by severing a running web of cigarette paper, imitation cork or like strip-shaped material (called tipping paper) at regular intervals to form a succession of discrete uniting bands. Successive uniting bands are attached to and rolled around groups of coaxial filter plugs and cigarettes in a suitable filter tipping machine, such as the machines known as MAX or MAX S manufactured and sold by the assignee of the present invention.
If the perforations are to be formed in the wrapper of a plain cigarette, they are normally provided close to that end of the cigarette which is inserted into the mouth during smoking.
It is also known to make perforations by resorting to an apparatus which is equipped with one or more lasers. Reference may be had to German Offenlegungsschrift No. 2,754,104. It has been found that coherent radiation which is emitted by a laser is especially suited to ensure the formation of perforations having a predictable size and/or shape, as well as that a laser is capable of perforating a rapidly running web of cigarette paper or the like. Perforating apparatus which employ one or more lasers are further disclosed in commonly owned U.S. Pat. Nos. 4,193,409 and 4,249,545, and in commonly owned U.S. patent application Ser. No. 834,648 filed Sept. 19, 1977 by Heitmann et al.
A drawback of presently known perforating apparatus is that they are likely to become contaminated, for example, by the material which is separated from the running web during making of the perforations therein. The contamination is likely to occur regardless of whether the apparatus employs one or more mechanical perforating devices, one or more electrical perforating devices (e.g., pairs of electrodes which define spark gaps through which the material of the running web is advanced) or one or more lasers or other sources of coherent radiation. Such contamination necessitates frequent interruptions in operation of the machine in which the perforating apparatus is installed. This is especially undesirable if the machine is a modern high-speed maker of cigarettes or filter rods because such machines turn out inordinately large quantities of rod-shaped articles per unit of time (e.g., a modern cigarette maker can produce up to and in excess of 100 plain cigarettes per second) so that each and every interruption of operation of such a machine entails tremendous losses in output.